Non-thermal plasma coupled with MO_x/-Al₂O₃ (M: Fe, Co, Mn, Ce) for chlorobenzene degradation: Analysis of byproducts and the reaction mechanism

Chlorinated volatile organic compounds (VOCs) such as chlorobenzene pose serious human health and environmental risks, but are resistant to elimination techniques that are traditionally applied to Cl-free VOCs. Nonthermal plasma (NTP) offers a promising technique to decompose chlorobenzene, but its application remains limited owing to low COx selectivity and the generation of toxic byproducts. To address these problems, this study investigated chlorobenzene degradation in NTP coupled with MOx/gamma-Al2O3 (M: Fe, Co, Mn, Ce) catalysts. The combination of NTP with MOx/gamma-Al2O3 remarkably improved the removal efficiency (RE), mineralization rate (MR), Cl selectivity (Su) and energy yield (EY) of chlorobenzene abatement, and decreased the production of residual O-3. CoOx/gamma-Al2O3 exhibited the best performance among these tested catalysts with higher RE, MR, S-Cl and EY by 26.06%, 25.52%, 33.03% and 2.41 g/kWh, respectively, at 510 J/L, compared with those of the NTP alone system. Several catalyst characterizations were applied to explore the relation between the catalyst characteristics and chlorobenzene abatement efficacy in NTP. The results indicate that the NTP catalytic oxidation of chlorobenzene strongly depends on the reducibility and acidity of the MOx/gamma-Al2O3 samples, whereas the textural properties of the catalysts exert a limited influence on chlorobenzene degradation. Highresolution gas chromatography and high-resolution mass spectrometry analyses verified for the first time that PCDD/Fs were generated during chlorobenzene degradation in NTP catalytic reactions. A plausible decomposition mechanism of chlorobenzene in the NTP catalytic system is speculated according to the organic intermediates generated during chlorobenzene decomposition.